Melanopsin is a putative photopigment recently shown to be present in a small subset (1-2%) of intrinsically photosensitive retinal ganglion cells in rat and mouse. These cells project to non-image-forming visual centers in the brain, such as the suprachiasmatic nucleus, the intergeniculate leaflet and the olivary pretectal nucleus. The long-term objective of this proposal is to understand the structure and function of the melanopsin-associated visual pathway in detail. The specific aims are: 1) To map the projections of the melanopsin-containing retinal ganglion cells to the mouse brain in detail, 2) To assess the contribution of melanopsin-associated signaling versus that of rod/cone signaling to non-image-forming visual functions in mouse, 3) To study the light responses and the phototransduction mechanism of the intrinsically photosensitive, melanopsin-expressing retinal ganglion cells, and 4) To study the characteristics of the melanopsin-expressing retinal neurons in primates and other vertebrates. The experimental approach will combine mouse genetics, cell biology, electrophysiology and some collaborative whole-animal physiological and behavioral experiments.